Furfural is an aromaticaldehyde, with the ring
structure shown at right. Its chemical
formula is C5
H4 O2. In its pure state, it is a
colorless oily liquid with the odor of almonds, but upon exposure to air
it quickly becomes yellow.

History

Furfural was first isolated in 1832 by the Germanchemist
Johann Wolfgang Döbereiner, who formed a very small quantity of
it as a byproduct of formic acid
synthesis. At the time, formic acid was formed by the distillation of dead
ants, and Döbereiner's ant
bodies probably contained some plant matter. In 1840, the Scottish chemist
John
Stenhouse found that the same chemical could be produced by
distilling a wide variety of crop materials, including corn, oats,
bran, and sawdust, with aqueous sulfuric
acid, and he determined that this chemical had an empirical
formula of C5H4O2. In 1901, the German chemist Carl Harries
deduced furfural's structure.

Except for occasional use in perfume, furfural remained a
relatively obscure chemical until 1922, when the Quaker
Oats Company began mass-producing it from oat hulls. Today,
furfural is still produced from agricultural byproducts like
sugarcane bagasse and
corn cobs.

Properties

Furfural's physical properties are summarized in
the table at right. Furfural dissolves readily in most polar
organic
solvents, but is only slightly soluble in either water or alkanes.

Chemically, furfural participates in the same
kinds of reactions as other aldehydes and other aromatic compounds.
The aromatic stability of furfural is not as great as in benzene, and furfural
participates in hydrogenation and other
addition
reactions more readily than many other aromatics.

When heated in the presence of acids, furfural
irreversibly solidifies into a hard thermosetting resin.

Production

Many plant materials contain the polysaccharidehemicellulose, a polymer of sugars containing five carbon
atoms each. When heated with sulfuric acid, hemicellulose undergoes
hydrolysis to yield
these sugars, principally xylose. Under the same conditions
of heat and acid, xylose and other five carbon sugars undergo
dehydration, losing three water molecules to become furfural:

For crop residue feedstocks, about 10% of the
mass of the original plant matter can be recovered as furfural.
Furfural and water evaporate together from the reaction mixture,
and separate upon condensation.

Global total capacity of production is about
450,000 ton. China is the biggest
supplier of this product and they have about a half of global
capacity.

In the laboratory, synthesis of furfural from
corn cobs takes place by reflux with dilute sulfuric
acid .

Chronic skin exposure can lead to a skin allergy to the substance, as
well as an unusual susceptibility to sunburn. In toxicity studies,
furfural has led to tumors, mutations, and liver and kidney damage in animals.